Switching circuit



United States Patent i 2,996,628 SWITCHING CIRCUIT Dietrich Holz, Berlin, Germany, assignor to VEB Werk fiir Signalund Sicherungstechnik Berlin, Berlin-Treptow, Germany Filed Aug. 30, 1957, Ser. No. 681,225

Claims priority, application Germany Nov. 19, 1956 2 Claims. (Cl. 30'7-88) This invention relates to switching circuits and more particularly to circuits in which loads are selectively coupled to power sources.

A typical example of a circuit in which loads are selectively switched into the circuit of a power supply is the signal lamp circuit of a railroad warning system. For example, red, green and amber lamps are employed to indicate various conditions attendant to railway operations and these lamps are selectively connected to an electrical power source for purposes of illumination. Moreover, additional lamps may be provided in such a system to become effective upon the failure of one or more of the normally employed lamps.

in the type of circuit indicated above, the lamps are not only selectively coupled to a power source, but they are furthermore selected in a particular manner. Thus, for example, if one load is rendered inoperative, such as by the opening of the green lamp in the railway system due to the passing of a rail vehicle, the next load such as the amber lamp should be automatically rendered operative. Moreover, in the event of an emergency, an auxiliary load or lamp is preferably connected immediately to the power source.

One known system of selectively rendering loads effective involves the utilization of rnulti-phase networks wherein an interruption in a loaded circuit is reflected by a current increase due to the decrease of the induced counter which is employed to switch in a substitute load. This type of system has further been developed to distinguish between different voltage increments so as to selectively substitute loads.

It is, however, an object of the invention to provide an improved system which avoids the necessity of depending upon expensive multi-phase circuits.

It is, furthermore, an object of the invention to avoid the deficiencies inherent in multi-phase circuits such as, for example, coincidence in phases whereby the switching function is not performed and the possible failure of responding to short circuiting of loads i.e. failure of melting the fuse because of the high reactance hitherto necessarily forming part of the circuit.

The multi-phase type of circuit despite its insufiiciences is never-the-less typical of load switching systems which desirably perform their functions without relying upon mechanically operated switches.

Accordingly, it is a further object of the invention to achieve its advantages while at the same time providing a contactless type of apparatus exclusive, of course, of other types of switches which may be employed in the associated system.

Briefly, the invention contemplates achieving its various objectives by the provision of a system in which use is made of magnetic amplifiers. In accordance with one embodiment of the invention, loads such as signal lamps are selectively substituted for one another by employ- 2,996,628 Patented Aug. 15, 1961 ing the windings associated with magnetic amplifiers as impedances in series with the loads. These windings can be subjected to conditions during which they are characterized by high or low impedances and these conditions are utilized to render the loads effective and ineffective.

Advantageously, the systems enabled by the invention need not rely upon mechanical switches. Furthermore, since multiphase power sources need not be used, the deficiencies of the required associated circuits are avoided. These and other objects and advantages of the invention will next be set forth 'in the following detailed description as illustrated in the sole figure of the accompanying drawing in which is shown the schematic diagram of a railway warning system employing contactless switching devices in accordance with the invention.

In the drawing are shown, by way of example, four signal lamps '10, r12, 14 and F16. A greater number of or fewer lamps can be employed, but four have been indicated to cover green, amber and red signal lamps as well as an auxiliary lamp which is illuminated in the event of special emergencies. The indications intended by the use of the different colors are well known.

Associated with the lamps 10, 12, 1-4, 16 are the magnetic amplifiers 18, 20 and 22. Generally, it can be considered that the necessary number of magnetic amplifiers is one less than the number of loads to be controlled.

Each magnetic amplifier, the details of which will subsequently be described, includes a magnetizable core and at least two windings in magnetically bucking relationship thereon. Thus, the flow of current through both of the windings at the same time results in a cancellation of the magnetic effect of the two windings whereas only the flow of current through a single winding can cause a mag netization of the core.

The magnetized or demagnetized condition of the cores is usefully employed in connection with the windings whose impedances are determined by whether or not the associated cores are saturated with flux. Thus, when any one of the cores is saturated with magnetic flux, the impedance of the associated windings is minimized whereas, when the core is demagnetized, the impedance of the associated windings or coils is maximized. These variable impedances are used to control the flow of current through the lamps 1t 12, 14, 16.

The lamps are adapted to be illuminated by means of the source of electrical power 24 which is, in the illustration, a source of alternating-current power. Lamps 14 and 116 are directly coupled to the source 24 by the line 26 via branch lines 28 and 30 whereas lamps 10 and 12 are coupled to the source 24 via branch lines 32 and 34 and switches 36 and 38.

The switches 36 and 38, which may be mechanical switches, are not the switches referred to in the aforegoing brief description of the invention. 'Ihey are switches of known type such as, for example, switches which are associated with rails in a railway system and which are affected by the passing of a railway vehicle over a track. It will be assumed in the following description that these switches are normally closed whereupon power is supplied under normal circumstances simultaneously to all lamps, the circuit being substantially completed by the return line 40.

In the return line '40 are coupled the rectifier bridges 42, 44 and 46 which allow the use of an alternating-cur- J rent source. These bridges are, in known manner, constituted by rectifiers such as the rectifier 48.

Included in the magnetic amplifiers 18, 20, 22 are the cores 50af, the control windings 52af, load windings 54a-f and regenerative windings 56a-f. Also in the circuit are rectifiers 58af.

All of the magnetic amplifiers are wired in a similar manner, the wiring of the magnetic amplifier 18 being set forth by way of example. Typical of all the illustrated magnetic amplifiers, control windings 52a and b are connected in series but are separately wound on the respective cores 50a and b. These control windings are furthermore coupled across the rectifier bridge 42. A junction 60, directly coupled to the line 40, is connected, on the one hand, via the regenerative winding 56a, load winding 54b and rectifier 58b to the lamp 12 and, on the other hand, via the regenerative winding 56b, load winding 54a and rectifier 58a to the lamp 12. Windings 52a and 54a are wound so as to be in magnetically bucking relationship as are windings 52b and 54b in accordance with a function which will hereinafter be set forth and in accordance with predetermined directions of current flow. In contrast, windings 56a and b are intended to magnetically assist the magnetic effects of windings "52a and b at times when the associated windings 54a and b are ineffective.

As previously indicated, the magnetic condition of the cores Sim-f affects the impedances of the windings associated therewith. For a theoretical discussion of this phenomenon, reference may be made to Magnetic Amplifiers by H. G. Storn, John Wiley & Sons Inc, New York 1955). Briefly, however, when the cores are saturated with flux, the associated load windings will have a minimum impedance and when this saturated condition is removed the impedance is markedly increased.

Description of the operation of the system can be limited to the control of lamps and 12 inasmuch as the lamps 14 and 16 are respectively controlled by their associated control and load windings in a similar manner.

Assuming switches 36 and 38 to be closed, current tends to flow via lines 32 and 34 through lamps 1t) and Y12. The current flowing through the lamp 10 must necessarily flow through the control windings 52a and b of the magnetic amplifier 18 and, in fact, the current flowing through any lamp necessarily flows through the magnetic amplifiers associated with the following lamps. Thus, for example, the current passing through lamp 10 not only passes through windings 52a and b but also through windings 52c and 1. Due to rectifiers 58a and b, only one core 50 is effective at a given time depending upon the polarity of the voltage supplied by source 24 and according to the arrangement of the rectifiers 58 which are oppositely poled.

Considering, for example, core 500 with rectifier 58a conducting, the current tending to flow through lamps 10 and 12 will produce opposite and cancelling magnetic effects by means of windings 52a and 54a, there being no magnetic effect by the winding 56a due to the rectifier 58b. The impedance of load winding 54a will therefore be at a maximum. Current flow through the lamp 12 is therefore minimized.

If, however, current flow through the lamp 10 is terminated such as by the opening of switch 36 or by the burning out of lamp 10, the winding 52a no longer sets up a bucking magnetization in the core 5011 which then becomes saturated under the influence of winding 54a. During the opposite half cycle of the alternating current the same sequence occurs in the winding 52b, core Silb and winding 54b as previously occurred in the winding 52a, core 50a. and winding 54a. In this manner continuous flow of current is assured through the lamp 12.

' When this happens, the impedance of winding 54a is minimized and lamp 12 is illuminated; in this manner,

the lamps are selectively and sequentially made effective for operation as might any load be so controlled.

If current is interrupted by opening of switch 38, then the windings 52c and 52d of cores 50c and 50d of the magnetic amplifier 20 are deenergized. The identical sequence previously described as occurring for magnetic amplifier 18 occurs with respect to amplifier 20, so as to illuminate lamp 14. Analogously subsequent interruption of current through lamp 14 switches in the lamp 16 by way of magnetic amplifier 22.

The regenerative windings noted above are employed to minimize high voltage drops in the working circuits of the various magnetic amplifiers in an emergency.

Also included in the system are fuses 62 and 64 which serve protective functions in known manner. Fuse 62, however, further interrupts the flow of current through control windings 52a and 1 and consequently controls the illumination of lamp 16 when an emergency situation arises in the remainder of the system (:short circuit in one of the lamps 10, 12, 14).

There will now be obvious to those skilled in the art many modifications and variations of the circuitry set forth which do not depart essentially from the scope of the invention as defined in the following claims.

What is claimed is:

1. A circuit comprising an alternating current source, a plurality of loads each connected at one end to one terminal at said source, a plurality of full wave rectifier means having input and output terminals, said input terminals being connected in series from the other terminal of said source to the other terminal of a first of said loads, a plurality of circuit means each connecting the other ends of the remaining ones of said loads to the respective mutual junctions of said input terminals and to the terminal connected to said source; each of said circuit means including a pair of saturable reactors having a load winding, a control winding, and a core, first unidirectional current conducting means serially connecting one of said load windings to said load and to said respective input terminal, second unidirectional current conducting means serially connecting the other load winding to said load and to the respective terminal in parallel relation to the first load winding, said unidirectional means being oppositely poled whereby current flows in each winding during one half cycle; connecting means for energizing said control windings through the corresponding full wave rectifier means, said load windings being wound to buck said control windings whereby current flow through any load results in current flow through all rectifier means serially connected between that load and said source and causes desaturation of all reactor means controlled by said serially connected rectifier means and results in inhibition of current flow through the corresponding loads.

2. A circuit comprising an alternating current source and a pair of loads across said source; a pair of saturable reactors each having a core, a control winding, a first series winding and a second series winding; first circuit means connecting said first series winding of the first of said saturable reactors in series with the second series winding of the second of said saturable reactors and in series with one of said loads, said circuit means including a first diode; second circuit means connecting said second series winding of the first of said saturable reactors in series with the first series winding of the second of said saturable reactors and in series with said first load so as to be in parallel with said first circuit means and the windings connected by said first circuit means; said second circuit means including a second diode poled opposite said first diode with respect to said first load; rectifier means having input means connected in series with the other of said loads and output means connected for supplying full wave rectified current to said control 5 6 windings; said first series windings being wound to buck first load; whereby upon current being interrupted in said the effects of said control windings and said second series second load said cores are saturated.

windings being Wound to assist the effects of said saturable windings in the respective saturable reactors; References C'ted m the file of thls patent whereby upon current passing through said second load 5 UNITED STATES PATENTS said control windings are excited and the current during 2 021,099 Fitzgerald Nov, 12, 1935 any half wave through at least one of said impedance 2,171,784 Dowling Sept. 5, 1939 windings causes bucking of the effects of said saturating 2,778,955 Isborn Jan. 22, 1957 windings in each of said saturable reactor thus unsaturat- 2,816,278 Whitely Dec. 10, 1957 ing said reactors and inhibiting current flow through said 10 2,873,438 Briganski Feb. 10, 1959 

